IS 3708 (Part 5) :2005 ISO 127:1995 *%'w- W$lm') Tmd&Rn%wMJTwf?Fi7 q $lTJT 5 ihfl-.wx. * m m Indian Standard METHODS PART 5 OF TEST FOR NATURAL RUBBER LATEX DETERMINATION OF KOH NUMBER (Second Revision ) ICS 83.040.10 @ 61S 2005 BUREAU MANAK OF INDIAN 9 BAHADUR STANDARDS SHAH ZAFAR MARG BHAVAN, NEW DELHI 110002 September 2005 Price Group 3 Rubber and Rubber Products Sectional Committee. PCD 13 NATK3NAL FOREWORD This Indian Standard (Part 5) (Second Revision) which is identical with ISO 127:1995 `Rubber, natural latex concentrate -- Determination of KOH number' issued by the International Organization for Standardization (ISO) was adopted by the Bureau of Indian Standards on the recommendations of the Rubber and Rubber Products Sectional Committee and approval of the Petroleum, Coal and Related Products Division Council. The text of ISO Standard has been proposed to be approved as suitable for publication as an Indian Standard without deviations. Certain conventions are, however, not identical to those used in Indian Standards. Attention is particularly drawn to the following: a) Wherever the words `International be read as `Indian Standard'. Comma practice Standard' appear referring to this standard, they should b) (,) has been used as a decimal marker while in Indian Standards, the current is to use a point (.) as the decimal marker. " The concerned Technical Committee has reviewd the provisions of the following International Standards referred in this adopted standard and has decided that they are acceptable for use in conjunction with this standard: International Standard Title Rubber latex -- Sampling Latex, rubber -- Determination of total sokk conteqt alkalinity ISO 123:2001 ISO 124:1997 ISO 125:1990 ISO 976:1996 ISO 1802:1992 Natural rubber latex concentrate -- Determinafti"of Rubber and plastics -- Polymer dispersion Determination of pH Natural rubber latex concentrate content temperature and rubber Iatices -- -- Determination of boric acid For tropical countries like India, the standard 27 * 2°C and 65 * 5 percent relatively. and the relative density shall be taken as For the purpose of deciding whether a particular requirement of this standard is complied with the final value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance with IS 2:1960 `Rules for rounding off numerical values (revised)'. The number of significant places retained in the rounded off value should be the same as that of the specified value in this standard. IS 3708 (Part 5) :2005 ISO 127:1995 Indian Standard METHODS OF TEST FOR NATURAL RUBBER LATEX PART 5 DETERMINATION OF KOH NUMBER (Second Revision ) WARNING -- Persons using this standard should be femiliar with normel laboratory prectice.This standard does not purport to address all of the safety problems, if any, associatedwith its use. It is the resnonsibilitv of the user to establish appropriate safety end health practicesand to ensure compliancewith-any national regulatory conditions. 1 Scope for the rubber in part ISO 125:1880, Natural rubber latex concentrate termination of alkalinity ISO 976:-- 1), Rubber Iatices -- Determination -- De- Iatices containing boric acid. The method is not applicable to Iatices preserved with potassium hydroxide. It is not necessarily suitable for Iatices from natural sources other tha; Hevea brasiliensis, or for Iatices of synthetic rubber, compounded latex, vulcanized latex or artificial dispersions of rubber. This International Standard specifies a method determination of tne KOH number of natural latex concentrate which is presewed wholly or with ammonia. The method is applicable to of PH. -- ISO 1802:1885, Natura/ rubber /atex concentrate Determination of boric acid content. 3 Definition For the purposes of this International Standard, the following definition applies. 2 Normative references 3.1 KOH number (of latex):The number of grams of potassium hydroxide equivalent to the acid radicals combined with ammonia in latex concentrate containing 100 g of total solids. (Definition taken from cabulary/Add.2:1982.) ISO 1382:1982, Rubber -- VO- The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 123:1985, Rubber /atex -- Sampling. of total 4 Reagents During the analysis, use only reagents of recognized analytical grade and only distilled water free of dissolved carbon dioxide, or water of equivalent purity. ISO 1241992, Rubber Iatices -- Determination solids content. 1) To be published. IS 3708 ISO (Part 5) :2005 127:1995 4.1 Potassium hydroxide, standard volumetric solution, c(KOH) = 0,1 mol/dm3, carbonate-free. Carry out the determination in duplicate. Weigh, to the nearest 0,1 g, into a 400 cm3 beaker a test portion (mass m) of the test sample containing approximately 50 g of total solids. If necessa~, adjust the alkalinity to (0,5 * 0,1 ) % ammonia calculated with respect to the water phase by adding, while stirring, the required quantity of formaldehyde solution (4.3). Calculate the volume of formaldehyde solution to be added from the formula m(l 00WTS)(A 4.2 Potassium hydroxide, standard volumetric solution, c(KOH) = 0,5 mol/dm3, carbonate-free. 4.3 Formaldehyde,45 g to 50 g in 1 dm3 of solution Ic(HCHO) = 1,5 mol/dm3 to 1,67 moi/dm31, acid-free, prepared by diluting concentrated formaldehyde with water and neutralizing with 0,1 mol/dm3 potassium hydroxide solution (4.1 ), using as indicator the faint pink colour of phenolphthalein. Determine the concentration of the solution as described in annex A. formaldehyde -O, 5) 1134C(HCHO) when? c(HCHO) is the actual concentration, expressed in moles per cubic decimetre, of the formaldehyde solution (4.3). iXlute the latex with water to about 30 % total solids. lnseR the electrodes of the pH-rneter (5.1) into the diluted latex concentrate and record the PH. glassware, plus the following: 5 Apparatus Standard laboratory 5.1 pH-meter,conforming being read to 0,01 units. to ISO 976 but capable of If the initiil pH k 16as ?han' 16,3, akwvty add 5 cms of 0,5 mol/dr# potassium hydroxide solution (4.2) while stirring slowly with the glass paddle or magnetic stirrer (5.3). Record the resultant equilibrium pH reading. Whh continued stirring, add 0,5 moi/dr# potassium hydroxide solution (4.2) in 1 cr# increments at regular (e.g. 15s) intervals, recording ths resultant equilibrium pH after each addition. Continua until the end-point has been passed. If the initial pH is 10,3 or higher, omit the initial addition of 5 cm3 at one time and proceed directly to "add 0,5 mol/dms potassium hydroxide solution (4.2) in 1 cms increments" as described above. Glass alectrode,of a type 5.2 solutions of pH up to 12,0. suitable for use in 5.3 Mechanical stirrar, with earthed glass paddle, or magneticstirrer. motor and The end-point of the titration is the point of inflf?XiOt7 Of NOTE 1 An automatic titrator may be used provided it has been checked as giving the same result as the standard method. 6 Sampling with one of the the titration curve of the pH-value against. the volume, in cubic centimetres, of potassium hydroxide solution. At this point, the slope of the curve, i.e. the first differential, reaches a maximum and the second differential changes from a pasitive to a negative value. The end-point shall be calculated from the second differential on the assumption that the change from a positive to a negative value bears a linear reiation to the addition of potassium hydroxide during the 1 cm3 intewal involved. An example of a typical titration and the calculation the end-point is given in annex B. The results of duplicate within 5 `Yo (m/m). determinations of Carry out the sampling in accordance methods specified in ISO 123. shall agree to 7 Procedure Calibrate the pH-meter by the method specified in ISO 976. If the total solids (WTJ and alkalinity W of the latex are not known, determine them in accordance with ISO 124 and ISO 125 respectively. If the latex contains boric acid and the content is not known, determine it in accordance with ISO 1802. 8 Expression of results Calculate the KOH number, expressed as a percentage by mass, of the latex concentrate from the formula 2 IS 3708 (Part 5) :2005 ISO 127:1995 561c.v w~~ m where c is the actual concentration, expressed in moles of KOH per cubic decimetre, of the potassium hydroxide solution (4.2); is the volume, in cubic centimetres, of the nominally 0,5 mol/dm3 potassium hydroxide solution (4.2) required to reach the end-point; 91X$ where WBA is the boric acid content, percentage by mass. expressed as a 9 Test report The test report shall include the following a) b) c) d) e) f) g) a reference to this International information: V Standard; identification identification of of wT~ is the total solids content, expressed as a percentage by mass, of the latex concentrate; m is the mass, in grams, of the test portion. all details necessa~ the sample; all details necessary the pH-meter used; the result obtained; the correction for complete for complete If the latex concentrate contains boric acid, subtract the KOH number equivalent to the boric acid from the KOH number obtained above. Calculate the KOH number equivalent to the boric acid present from the formula applied for boric acid, if present; details of any operation not included in this international Standard or regarded as optional; the date of the test. IS 3708 (Part 5) :2005 ISO 127:1995 Annex A (informative) Determination of formaldehyde The method given in previous editions of this international Standard appears not to have been widely used due to the fact that standard solutions of ammonia are considered to be unsatisfactory. Having regard to the consistent quality of analytical-grade concentrated formaldehyde solution, the majority of users prepare a standard solution of formaldehyde directly. Where it is necessary to determine the concentration of the diluted formaldehyde, a variety of methods exist and users are referred to the Encyc/opaedia of by Industrial Chemical Analysis, Vol. 13, published Interscience (1971). The method given below is for information only. Transfer 100 cms of the solution to a flask. Accurately weigh into the flask the nominally 50 g/dins formaldehyde and swirl to mix thoroughly. Allow to 500 cm3 conical 6,0 g to 8,0 g of solution (4.3)2, stand for 5 rein, then titrate with 0,25 mol/dm3 sulfuric acid (Al .2) to the first colorless end-point using thymolphthalein (Al .3) as indicator. Run a blank determination with the soldium sulfite solution. A.3 Expression of results A.1 A.1.1 A.1.2 Reagents Sodium sulfite,anhydrous, Sulfuric acid, standard analytical grade. Calculate the formaldehyde content, expressed as a percentage by mass, of the formaldehyde solution from the formula 30,03(VI - Vz) x 2c(HzS04) 1Oml where volumetric solution, C(H2S04) = 0,25 mol/dm3. A.1.3 Thymolphthalein, indicator solution. Dissolve 80 mg of thymolphthalein in 100 cm3 of ethyl alcohol and dilute with 100 cm3 of distilled water. v, is the volume, in cubic centimetres, of sulfuric acid (Al .2) used for the titration of the test portion of formaldehyde solution; is the volume, in cubic centimetres, of sulfuric acid (A. 1.2) required for the blank; in moles of of the sul- v* A.2 Procedure C(H2SOJ is the actual concentration, H2S04 per cubic decimetre, furic acid; ml Prepare a solution of 125 g of anhydrous sodium sulfite (Al.1 ) in 500 cm3 of water and dilute to 1 dins. is the mass, in grams, of the test portion of formaldehyde solution. 2) When analysing concentrated formaldehyde solution, 1,8 g to 2,0 g of solution is a more convenient amount to take 4 IS 3708 (Part 5) :2005 ISO 127:1995 Annex B (informative) Example of a typical titration and calculationof end-point TableB.1-- Exampleof a typicaltitrationto show variationin pH Volumeof KOH solutionaddad cm3 pH reading Firstdifference ApH/cm3 Seoonddiffarenoe A2pH/cm3 Initial 10,09 5 6 7 8 10,46 0,09 10,55 0,10 10,65 0,11 10,76 0,01 0,01 0,03 0,14 0,04 0,18 0,06 0,24 0,07 0,31 ­0,01 0,30 ­0,09 0,21 9' 10 11 12 10,90 11,08 11,32 11,63 11,93 12,14 13 14 In this example, the first difference reaches a maximum of 0,31 between 11 cms and 12 cms of potassium hydroxide solution. The precise point of inflexion is calculated from the ratio of the adjacent seconddifference values, i.e. 0,07/(0,07 + 0,01) = 0,875 of the difference between 11 cms and 12 cm3, i.e. 11,875 ems. Figure B. 1 presents this data graphically to show the point of inflexion, 5 IS 3708 (Part 5) :2005 ISO 127:1995 12,2~ 12 !' /' It /1 11,8End-point 11,6- 11,4- 11,2- 11 10,8- 10,6 - loA~ 567891011 Volume of potossium hydroxide 1213V+ solution (cm') Figure B.1 -- Illustrative curve showing change of pH during titration Bureau of Indian Standards institution established of the activities matters under the Bureau of Indian Standards marking and quality Act, 1986 BIS is a statutory harmonious and attending to promote of goods development to connected of standardization, certification in the country. Copyright BIS has the copyright without the prior of all its publications. No part of these publications maybe reproduced in any form in writing of BIS. This does not preclude the free use, in the course of implementing the standard, of necessary details, such as symbols and sizes, type or grade designations. Enquiries relating to copyright be addressed to the Director (Publications), BIS. permission Review of Indian Standards Amendments are issued to standards as the need arises on the basis of comments. Standards are also reviewed periodically; a standard along with amendments is reaffirmed when such review indicatesthat no changes are needed; if the review indicates that changes are needed, it is taken up for revision. Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition by referring to the latest issue of `BIS Catalogue' and `Standards: Monthly Additions'. This Indian Standard has been developed from Doc: No. pCD 13 (1998). 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